KR0182018B1 - Common electrode substrate and manufacturing method of liquid crystal display device - Google Patents

Abstract

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Description

Common electrode substrate of liquid crystal display apparatus and manufacturing method thereof

FIG. 1 is a cross-sectional view showing a common electrode substrate of a conventional liquid crystal display device,

FIGS. 2 to 17 are cross-sectional views showing a common electrode substrate of a liquid crystal display device according to a first embodiment of the present invention,

17 to 24 are cross-sectional views showing a common electrode substrate of a liquid crystal display device according to a second embodiment of the present invention.

The present invention relates to a common electrode substrate of a liquid crystal display device and a method of manufacturing the common electrode substrate, and more particularly, to a common electrode substrate of a liquid crystal display device having a compensating film for compensating for a phenomenon in which light is leaked due to optical anisotropy of liquid crystal, .

In general, a panel of a liquid crystal display device includes a glass substrate, three color filter layers of red, green and blue, and a common electrode substrate including a common electrode, a plurality of pixels, a data line for transmitting an image information signal to the pixel, A thin film transistor substrate formed at an intersection of the data line and the gate line, and a liquid crystal filled between the thin film transistor substrate and the common electrode substrate.

FIG. 1 is a cross-sectional view showing a common electrode substrate of a conventional liquid crystal display device.

1, the structure of the common electrode substrate of the liquid crystal display device includes a substrate 10 made of a transparent insulating material, a red filter layer R and a green filter layer (not shown) formed on the substrate 10, And a common electrode 14 formed on the color filter layer 12 and made of a transparent conductive material. The color filter layer 12 may be formed of a transparent conductive material.

Conventional liquid crystal display devices having such a structure use a twisted-nematic (TN) liquid crystal material, and thus have a viewing angle dependence on optical transmittance.

Therefore, a gradation error occurs depending on the viewing angle. Gradation errors increase as the viewing angle increases and limit the viewing angle. Such an angle dependency is caused by the characteristics of the liquid crystal director, and is particularly severe in the up and down direction, and has a disadvantage of exhibiting asymmetric visual characteristics.

The reason for this phenomenon is that the light polarized parallel to the director of the liquid crystal due to the anisotropy of the nematic liquid crystal proceeds at a different speed than the light polarized perpendicular to the director.

Namely, a nematic liquid crystal is a birefringent material. This feature is best seen when the liquid crystal is between crossed polarizers.

If there is no material between the two polarizers, there is no light from the normally crossed polarizer, because the light passing through the first polarizer is completely absorbed by the second polarizer.

Insertion of an isotropic material does not change the polarization of the light as it travels through the isotropic material, so no change occurs.

However, if there is a nematic liquid crystal between two polarizers, if the polarized light from the first polarizer is in a direction different from 0 ° or 90 ° from the direction of the liquid crystal, the two polarized lights are different in phase when they pass through the liquid crystal, It appears as a light.

In other words, if there is no liquid crystal between the polarizers, it will appear dark, but when the liquid crystal is placed between the polarizers, the view generally appears bright. This effect was discovered by O. Lehmann, and it can be concluded that the liquid crystal is an anisotropic substance.

It appears generally bright between polarizers where liquid crystals intersect, but dark under the following two conditions.

If the polarized light incident on the liquid crystal is polarized in a horizontal or vertical direction to the director of the liquid crystal, light polarized at 90 degrees to this direction need not be considered since all light is polarized in one direction only in the liquid crystal.

Eventually, the light travels through the liquid crystal at one speed and is polarized in only one direction. Thus it is removed by the second polarizer.

On the other hand, the liquid crystal has anisotropy in that the physical properties such as electric susceptibility and magnetic susceptibility are different in the direction of the director and in the direction perpendicular thereto, This is because the rod-shaped molecules, which are not spatially symmetric, have a directional order to align them in a certain direction.

For example, the permittivity also depends on the direction since the rate of electricity acceptance differs from the direction of the director to the direction perpendicular to it. The dielectric constant in the liquid crystal director direction The dielectric constant in a direction orthogonal thereto In other words,

, The former has a positive (p-type) dielectric anisotropy, and the latter has a negative (n-type) negative dielectric anisotropy. When n is a direction, electric displacement D when a direct current electric field E is applied,

Therefore, the electrostatic energy,

. In the case of a liquid crystal with a positive dielectric constant anisotropy, that is, in the case of Δε0, it is stable when the director is parallel to the electric field, and when the director has a negative dielectric anisotropy, When it is stable. Therefore, in the case of a positive dielectric constant anisotropic liquid crystal, the directors tends to arrange parallel to the applied electric field, while in the case of a negative dielectric anisotropic liquid crystal, it tends to arrange perpendicularly to the applied electric field.

On the other hand, another characteristic of liquid crystal according to anisotropy is birefringence phenomenon. This will be described in detail.

Light has an electric field and a magnetic field that oscillate perpendicular to its direction of travel. Also, the direction of the electric field and the magnetic field are perpendicular to each other. If the electric field in the electromagnetic wave indicates only one direction in space, it is said to be linearly polarized.

Then, let us consider the case where linearly polarized light is incident on a medium other than a vacuum in a vacuum. If the medium is a homogeneous isotropic medium, the light travels straight in one direction even if the angle is changed by refraction.

However, in the case of liquid crystalline materials with optical anisotropy, the situation is different. The light is obliquely incident on the director of the liquid crystal, and the light is not parallel or perpendicular to the director of the liquid crystal, and the linearly polarized light is incident obliquely with respect to the director of the liquid crystal, . Then, this light can be divided into a polarization component parallel to the incident surface and a polarization component perpendicular to the polarization plane. Let us first consider light with polarization parallel to the incident plane. As described above, since the dielectric constant in the direction parallel to the director of the liquid crystal is different from that in the direction perpendicular to the director, the refractive index (index of refraction) is also different. The refractive index in the direction parallel to the director And n is the refractive index in the vertical direction, the optical anisotropy [ _Delta] n is the refractive index difference in the two directions , And the velocities in the direction perpendicular to the director direction of this light are given by

to be. From here C is the flux in vacuum, and θ is the angle between the direction of the incident light and the direction of the beam. Therefore, this light is refracted. However, in the case of light vertically polarized at the interface, the velocity components in the direction of the molecular axis and in the vertical direction are And is not refracted.

Eventually, the light travels along two paths.

Generally, a ray not defined is called a normal ray, and a refracted ray is called an abnormal ray. Generally, since the incident light includes a light beam perpendicular to the interface and a light beam parallel to the interface, a normal light beam and an extraordinary light beam are generated for one incident light. This phenomenon is called birefringence. The axis in the direction in which birefringence does not occur is called the optical axis, and in the liquid crystal, it is the direction of the molecular axis.

As described above, the birefringence properties of the liquid crystal result in narrow viewing angles. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a liquid crystal display device in which a compensating film having a refractive index opposite to that of a liquid crystal is formed to compensate for a phenomenon in which light is leaked due to optical anisotropy of a liquid crystal A common electrode substrate and a method of manufacturing the same.

According to an aspect of the present invention,

A substrate made of a transparent insulating material, a first insulating film having a refractive index n ₁ and a second insulating film having a refractive index n ₂ (≠ n ₁ ), a compensation film formed on the substrate, And a common electrode formed of a material.

The compensating film may be formed on the common electrode, not between the substrate and the common electrode.

At this time, the refractive index n ₁ of the first insulating film and the refractive index n ₂ of the second insulating film are

.

In order to achieve the above object,

A first step of forming a double insulating film made of a second insulating film having a refractive index different from that of the first insulating film on a transparent insulating substrate; and a second step of forming a common electrode made of a transparent conductive material on the double insulating film.

On the other hand, the step of forming the compensating film may be performed first, and the step of forming the common electrode may be performed later.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

FIGS. 2 to 17 are cross-sectional views showing a common electrode substrate of a liquid crystal display device according to a first embodiment of the present invention,

17 to 24 are cross-sectional views showing a common electrode substrate of a liquid crystal display device according to a second embodiment of the present invention.

The common electrode substrate of the liquid crystal display according to the embodiment of the present invention has the following structure.

A compensating film 24 is formed on the substrate 20 made of a transparent insulating material and includes a first insulating film having a refractive index n ₁ and a second insulating film having a refractive index n ₂ (≠ n ₁ ) A common electrode 28 formed of a transparent conductive material is formed.

In this case, the thickness of each of the first insulating film and the second insulating film is preferably 200 to 500 ANGSTROM.

In addition, it is preferable that the compensation film 24 is formed by two or more layers of the double insulation film continuously, and more preferably, the double insulation film is formed continuously from 2 to 5 layers.

At this time, the compensation film 24 is preferably formed by the double SiOx insulating film and Al ₂ O _x or TaO _x and SiOx.

On the other hand, the compensation film 24 may be formed on the common electrode 28, not between the substrate 20 and the common electrode 28, as shown in FIG. 17.

As shown in FIG. 3, a color filter layer 22 is formed between the substrate 20 and the compensating film 24 to form a red filter layer, a green filter layer, and a blue filter layer at regular intervals, can do.

On the other hand, the color filter layer 22 can be formed between the common electrode 28 and the compensation film 24 as shown in FIG.

The color filter layer 22 may be formed between the substrate 20 and the common electrode 28, as shown in FIG. 18.

On the other hand, as shown in FIGS. 4 and 19, a black matrix 26 for covering the boundary between the color filter and the color filter layer 22 can be formed. At this time, the lower surface of the black matrix 26 is in contact with the substrate 20 and the side surface thereof is in contact with the color filter.

The black matrix 26 may be formed between the compensating film 24 and the common electrode 28, as shown in FIGS. 6 and 23.

The black matrix 26 may be formed between the compensating film 24 and the substrate 20 as shown in FIG. At this time, the lower surface of the black matrix 26 is in contact with the compensation film 24 and the side surface is in contact with the color filter.

The black matrix 26 may be formed between the compensating film 24 and the color filter layer 22 as shown in FIG. At this time, the lower surface of the black matrix 26 is in contact with the compensation film 24 and the side surface is in contact with the color filter.

The black matrix 26 is a double layer, and may be formed of CrO _x + Cr or TaO _x + Ta.

7 and FIG. 15, a protective film 30 may be formed between the compensation film 24 and the color filter layer 22.

The protective film 30 may be formed between the common electrode 28 and the color filter layer 22 as shown in FIG.

The common electrode 28 substrate of the liquid crystal display device in which both the black matrix 26 and the protective film 30 are formed has a black matrix 26 as shown in FIGS. 5, 14 and 20, The black matrix 26 may be located below the protective film 30 and the black matrix 26 may be located above the protective film 30 as shown in Figs. 8, 9, 16, Can be located.

The compensation film 24 of the substrate of the common electrode 28 of the liquid crystal display device having the above structure has the following conditions.

If the respective refractive indices in the n1, n2 are different two kinds of insulating film is a multilayer (MT), and the ordinary ray refractive index n _0, is changed to a single film properties is extraordinary ray refractive index having a n _e in nature. Here, the correlation is as follows.

The light passing through the multi-layer (MT) of the compensation film (24) generates normal and extraordinary rays due to birefringence phenomenon.

The normal ray refraction index n ₀ and the extraordinary ray refraction index n _e at this time can serve as the compensation film 24 when the following condition is satisfied.

Therefore the two materials constituting the multilayer (MT) can be formed by SiOx and Al ₂ Ox, TaOx or SiOx with.

As described above, the compensating film 24 made of the multi-layer (MT) can overcome the disadvantage that the optical anisotropy is negative and the optical anisotropy of the liquid crystal is positive so that the up and down viewing angles appear asymmetrically.

A method of manufacturing a common electrode substrate of a liquid crystal display device according to the present invention includes the following steps.

First, a compensating film 24 composed of two insulating films having different refractive indexes is formed on a substrate 20 made of a transparent insulating material.

Next, a common electrode 28 is formed on the compensating film 24.

The two insulating films of the compensating film 24 are preferably formed to have a thickness of 200 to 500 ANGSTROM.

The compensating film 24 forms two or more layers of two kinds of insulating films having different refractive indices continuously to form a multilayer (MT).

At this time, the multi-layer (MT) is preferably about 2 to 5 layers. In addition, the two kinds of insulating films constituting the multi-layer (MT) exhibit a film characteristic such as a single film having properties different from the original crystal structure when continuously deposited at 500 Å or less.

On the other hand, the step of forming the compensating film 24 may be performed first, and the step of forming the common electrode 28 may be performed later.

The compensation film 24 made of two insulating films having different refractive indexes is formed using reactive sputtering, photochemical deposition or photochemical or plasma enhanced nitridation and oxidation (photochemical or plasma enhanced nitridation and oxidation) .

Therefore, the effect of the present invention is to overcome the disadvantage that the image quality is deteriorated by the external light to realize low reflection, and the optical anisotropy of the compensation film becomes negative so that the optical anisotropy of the liquid crystal is positive, It can overcome the disadvantages that appear.

Claims (12)

A compensating film formed on the substrate, a compensating film formed on the compensating film, and a compensating film formed on the compensating film, the compensating film being formed of a first insulating film having a refractive index n ₁ and a second insulating film having a refractive index n ₂ (≠ n ₁ ) Wherein a refractive index n ₁ of the first insulating film and a refractive index n ₂ of the second insulating film satisfy a relationship of When you say, Wherein the first and second insulating films serve as a single film having a normal refractive index n ₀ and an extraordinary refractive index n _e . The common electrode substrate of claim 1, wherein each of the first insulating film and the second insulating film has a thickness of 200 to 500 ANGSTROM. The common electrode substrate of claim 1, wherein the compensating film comprises two or more layers of the double insulating film continuously. The common electrode substrate of claim 1, wherein the first insulating layer is made of SiOx, and the second insulating layer is made of Al ₂ O _x . The common electrode substrate of claim 1, wherein the first insulating layer is made of SiOx, and the second insulating layer is made of TaO _x . The liquid crystal display according to claim 1, further comprising a plurality of color filters including a plurality of red filters, a green filter, and a blue filter formed at regular intervals between the compensating film and the substrate, Board. The common electrode substrate of claim 6, further comprising a black matrix for covering a boundary between the color filters. The common electrode substrate of claim 7, wherein the black matrix is a double layer and is made of CrO _x + Cr or TaO _x + Ta. A first step of forming a double insulating film composed of a first insulating film and a second insulating film different from the first insulating film on a transparent insulating substrate and a second step of forming a common electrode of a transparent conductive material on the double insulating film, The refractive index n ₁ of the insulating film and the refractive index n ₂ of the second insulating film are When you say, Wherein the first and second insulating films serve as a single film having a normal ray refraction index n ₀ and an extraordinary ray refraction index n _e . 10. The method of claim 9, wherein the first insulating layer and the second insulating layer are formed using reactive sputtering, photochemical deposition, photochemical or plasma nitridation and oxidation. A first step of forming a common electrode made of a transparent conductive material on a transparent insulating substrate and a second step of forming a double insulating film made of a second insulating film having a different refractive index from the first insulating film on the common electrode, The refractive index n ₁ of the second insulating film and the refractive index n ₂ of the second insulating film are When you say, Wherein the first and second insulating films act as a single film having a normal ray refractive index of no and an extraordinary ray refractive index of ne. 12. The method of claim 11, wherein the first insulating film and the second insulating film are formed using reactive sputtering, photochemical deposition, photochemical or plasma nitridation and oxidation.